To support progressive tumor growth beyond the size of 1-2 mm3, it is recognized that tumor cells require a functional stroma, a support structure consisting of fibroblast, smooth muscle cells, endothelial cells, extracellular matrix proteins, and soluble factors (Folkman, J., Semin Oncol, 2002. 29(6 Suppl 16), 15-8). Tumors induce the formation of stromal tissues through the secretion of soluble growth factors such as PDGF and transforming growth factor-beta (TGF-beta), which in turn stimulate the secretion of complimentary factors by host cells such as fibroblast growth factor (FGF), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF). These stimulatory factors induce the formation of new blood vessels, or angiogenesis, which brings oxygen and nutrients to the tumor and allows it to grow and provides a route for metastasis. It is believed some therapies directed at inhibiting stroma formation will inhibit the growth of epithelial tumors from a wide variety of histological types. (George, D. Semin Oncol, 2001. 28(5 Suppl 17), 27-33; Shaheen, R. M., et al., Cancer Res, 2001. 61(4), 1464-8; Shaheen, R. M., et al. Cancer Res, 1999. 59(21), 5412-6). However, because of the complex nature and the multiple growth factors involved in angiogenesis process and tumor progression, an agent targeting a single pathway may have limited efficacy. It is desirable to provide treatment against a number of key signaling pathways utilized by tumors to induce angiogenesis in the host stroma. These include PDGF, a potent stimulator of stroma formation (Ostman, A. and C. H. Heldin, Adv Cancer Res, 2001, 80, 1-38), FGF, a chemo-attractant and mitogen for fibroblasts and endothelial cells, and VEGF, a potent regulator of vascularization.
PDGF is another key regulator of stromal formation which is secreted by many tumors in a paracrine fashion and is believed to promote the growth of fibroblasts, smooth muscle and endothelial cells, promoting stroma formation and angiogenesis. PDGF was originally identified as the v-sis oncogene product of the simian sarcoma virus (Heldin, C. H., et al., J Cell Sci Suppl, 1985, 3, 65-76). The growth factor is made up of two peptide chains, referred to as A or B chains which share 60% homology in their primary amino acid sequence. The chains are disulfide cross linked to form the 30 kDa mature protein composed of either M, BB or AB homo- or heterodimmers. PDGF is found at high levels in platelets, and is expressed by endothelial cells and vascular smooth muscle cells. In addition, the production of PDGF is up regulated under low oxygen conditions such as those found in poorly vascularized tumor tissue (Kourembanas, S., et al., Kidney Int, 1997, 51(2), 438-43). PDGF binds with high affinity to the PDGF receptor, a 1106 amino acid 124 kDa transmembrane tyrosine kinase receptor (Heldin, C. H., A. Ostman, and L. Ronnstrand, Biochim Biophys Acta, 1998. 1378(1), 79-113). PDGFR is found as homo- or heterodimer chains which have 30% homology overall in their amino acid sequence and 64% homology between their kinase domains (Heldin, C. H., et al. Embo J, 1988, 7(5), 1387-93). PDGFR is a member of a family of tyrosine kinase receptors with split kinase domains that includes VEGFR2 (KDR), VEGFR3 (Flt4), c-Kit, and FLT3. The PDGF receptor is expressed primarily on fibroblast, smooth muscle cells, and pericytes and to a lesser extent on neurons, kidney mesangial, Leydig, and Schwann cells of the central nervous system. Upon binding to the receptor, PDGF induces receptor dimerization and undergoes auto- and trans-phosphorylation of tyrosine residues which increase the receptors' kinase activity and promotes the recruitment of downstream effectors through the activation of SH2 protein binding domains. A number of signaling molecules form complexes with activated PDGFR including PI-3-kinase, phospholipase C-gamma, src and GAP (GTPase activating protein for p21-ras) (Soskic, V., et al. Biochemistry, 1999, 38(6), 1757-64). Through the activation of PI-3-kinase, PDGF activates the Rho signaling pathway inducing cell motility and migration, and through the activation of GAP, induces mitogenesis through the activation of p21-ras and the MAPK signaling pathway.
In adults, it is believed the major function of PDGF is to facilitate and increase the rate of wound healing and to maintain blood vessel homeostasis (Baker, E. A. and D. J. Leaper, Wound Repair Regen, 2000. 8(5), 392-8; Yu, J., A. Moon, and H. R. Kim, Biochem Biophys Res Commun, 2001. 282(3), 697-700). PDGF is found at high concentrations in platelets and is a potent chemoattractant for fibroblast, smooth muscle cells, neutrophils and macrophages. In addition to its role in wound healing PDGF is known to help maintain vascular homeostasis. During the development of new blood vessels, PDGF recruits pericytes and smooth muscle cells that are needed for the structural integrity of the vessels. PDGF is thought to play a similar role during tumor neovascularization. As part of its role in angiogenesis PDGF controls interstitial fluid pressure, regulating the permeability of vessels through its regulation of the interaction between connective tissue cells and the extracellular matrix. Inhibiting PDGFR activity can lower interstitial pressure and facilitate the influx of cytotoxics into tumors improving the anti-tumor efficacy of these agents (Pietras, K., et al. Cancer Res, 2002. 62(19), 5476-84; Pietras, K., et al. Cancer Res, 2001. 61(7), 2929-34).
PDGF can promote tumor growth through either the paracrine or autocrine stimulation of PDGFR receptors on stromal cells or tumor cells directly, or through the amplification of the receptor or activation of the receptor by recombination. Over expressed PDGF can transform human melanoma cells and keratinocytes (Forsberg, K., et al. Proc Natl Acad Sci USA., 1993. 90(2), 393-7; Skobe, M. and N. E. Fusenig, Proc Natl Acad Sci USA, 1998. 95(3), 1050-5), two cell types that do not express PDGF receptors, presumably by the direct effect of PDGF on stroma formation and induction of angiogenesis. This paracrine stimulation of tumor stroma is also observed in carcinomas of the colon, lung, breast, and prostate (Bhardwaj, B., et al. Clin Cancer Res, 1996, 2(4), 773-82; Nakanishi, K., et al. Mod Pathol, 1997, 10(4), 341-7; Sundberg, C., et al. Am J Pathol, 1997, 151(2), 479-92; Lindmark, G., et al. Lab Invest, 1993, 69(6), 682-9; Vignaud, J. M., et al, Cancer Res, 1994, 54(20), 5455-63) where the tumors express PDGF, but not the receptor. The autocrine stimulation of tumor cell growth, where a large fraction of tumors analyzed express both the ligand PDGF and the receptor, has been reported in glioblastomas (Fleming, T. P., et al. Cancer Res, 1992, 52(16), 4550-3), soft tissue sarcomas (Wang, J., M. D. Coltrera, and A. M. Gown, Cancer Res, 1994, 54(2), 560-4) and cancers of the ovary (Henriksen, R., et al. Cancer Res, 1993, 53(19), 4550-4), prostate (Fudge, K., C. Y. Wang, and M. E. Stearns, Mod Pathol, 1994, 7(5), 549-54), pancreas (Funa, K., et al. Cancer Res, 1990, 50(3), 748-53) and lung (Antoniades, H. N., et al., Proc Natl Acad Sci USA, 1992, 89(9), 3942-6). Ligand independent activation of the receptor is found to a lesser extent but has been reported in chronic myelomonocytic leukemia (CMML) where the a chromosomal translocation event forms a fusion protein between the Ets-like transcription factor TEL and the PDGF receptor. In addition, activating mutations in PDGFR have been found in gastrointestinal stromal tumors in which c-Kit activation is not involved (Heinrich, M. C., et al., Science, 2003, 9, 9).
Certain PDGFR inhibitors will interfere with tumor stromal development and are believed to inhibit tumor growth and metastasis.
Another major regulator of angiogenesis and vasculogenesis in both embryonic development and some angiogenic-dependent diseases is vascular endothelial growth factor (VEGF; also called vascular permeability factor, VPF). VEGF represents a family of isoforms of mitogens existing in homodimeric forms due to alternative RNA splicing. The VEGF isoforms are reported to be highly specific for vascular endothelial cells (for reviews, see: Farrara et al. Endocr. Rev. 1992, 13, 18; Neufield et al. FASEB J. 1999, 13, 9).
VEGF expression is reported to be induced by hypoxia (Shweiki et al. Nature 1992, 359, 843), as well as by a variety of cytokines and growth factors, such as interleukin-1, interleukin-6, epidermal growth factor and transforming growth factor. To date, VEGF and the VEGF family members have been reported to bind to one or more of three transmembrane receptor tyrosine kinases (Mustonen et al. J. Cell Biol., 1995, 129, 895), VEGF receptor-1 (also known as flt-1 (fms-like tyrosine kinase-1)), VEGFR-2 (also known as kinase insert domain containing receptor (KDR); the murine analogue of KDR is known as fetal liver kinase-1 (flk-1)), and VEGFR-3 (also known as flt-4). KDR and fit-1 have been shown to have different signal transduction properties (Waltenberger et al. J. Biol. Chem. 1994, 269, 26988); Park et al. Oncogene 1995, 10, 135). Thus, KDR undergoes strong ligand-dependant tyrosine phosphorylation in intact cells, whereas flt-1 displays a weak response. Thus, binding to KDR is believed to be a critical requirement for induction of the full spectrum of VEGF-mediated biological responses.
In vivo, VEGF plays a central role in vasculogenesis, and induces angiogenesis and permeabilization of blood vessels. Deregulated VEGF expression contributes to the development of a number of diseases that are characterized by abnormal angiogenesis and/or hyperpermeability processes. It is believed regulation of the VEGF-mediated signal transduction cascade by some agents can provide a useful mode for control of abnormal angiogenesis and/or hyperpermeability processes.
The vascular endothelial growth factors (VEGF, VEGF-C, VEGF-D) and their receptors (VEGFR2, VEGFR3) are not only key regulators of tumor angiogenesis, but also lymphangiogenesis. VEGF, VEGF-C and VEGF-D are expressed in most tumors, primarily during periods of tumor growth and, often at substantially increased levels. VEGF expression is stimulated by hypoxia, cytokines, oncogenes such as ras, or by inactivation of tumor suppressor genes (McMahon, G. Oncologist 2000, 5(Suppl. 1), 3-10; McDonald, N. Q.; Hendrickson, W. A. Cell 1993, 73, 421-424)
The biological activities of the VEGFs are mediated through binding to their receptors. It is believed VEGFR3 (also called Flt-4) is predominantly expressed on lymphatic endothelium in normal adult tissues and that VEGFR3 function is needed for new lymphatic vessel formation, but not for maintenance of the pre-existing lymphatics. VEGFR3 is also upregulated on blood vessel endothelium in tumors. Recently VEGF-C and VEGF-D, ligands for VEGFR3, have been identified as regulators of lymphangiogenesis in mammals. Lymphangiogenesis induced by tumor-associated lymphangiogenic factors could promote the growth of new vessels into the tumor, providing tumor cells access to systemic circulation. Cells that invade the lymphatics could find their way into the bloodstream via the thoracic duct. Tumor expression studies have allowed a direct comparison of VEGF-C, VEGF-D and VEGFR3 expression with clinicopathological factors that relate directly to the ability of primary tumors to spread (e.g., lymph node involvement, lymphatic invasion, secondary metastases, and disease-free survival). In many instances, these studies demonstrate a statistical correlation between the expression of lymphangiogenic factors and the ability of a primary solid tumor to metastasize (Skobe, M. et al. Nature Med. 2001, 7(2), 192-198; Stacker, S. A. et al. Nature Med. 2001, 7(2), 186-191; Makinen, T. et al. Nature Med. 2001, 7(2), 199-205; Mandriota, S. J. et al. EMBO J. 2001, 20(4), 672-82; Karpanen, T. et al. Cancer Res. 2001, 61(5), 1786-90; Kubo, H. et al. Blood 2000, 96(2), 546-53).
Hypoxia appears to be an important stimulus for VEGF production in malignant cells. Activation of p38 MAP kinase is required for VEGF induction by tumor cells in response to hypoxia (Blaschke, F. et al. Biochem. Biophys. Res. Commun. 2002, 296, 890-896; Shemirani, B. et al. Oral Oncology 2002, 38, 251-257). In addition to its involvement in angiogenesis through regulation of VEGF secretion, p38 MAP kinase promotes malignant cell invasion, and migration of different tumor types through regulation of collagenase activity and urokinase plasminogen activator expression (Laferriere, J. et al. J. Biol. Chem. 2001, 276, 33762-33772; Westermarck, J. et al. Cancer Res. 2000, 60, 7156-7162; Huang, S. et al. J. Biol. Chem. 2000, 275, 12266-12272; Simon, C. et al. Exp. Cell Res. 2001, 271, 344-355).
The receptor tyrosine kinase Trk-A is another target of interest for the preparation of medicines directed at the treatment and prevention of cancer. TrkA is the high affinity receptor of the nerve growth factor (NGF). The expression of TrkA and NGF in tumors is believed to be implicated in the proliferation and metastasis of tumors such as pancreatic, prostate and also breast, as well as in angiogenesis. TrkA expression is reported in pancreatic, breast, ovarian, and prostate tumors. Recent studies demonstrate that human prostate and pancreatic tumor cells can secrete NGF, which, along with its receptor, TrkA, creates an autocrine loop that promotes the growth and survival of these tumor cells (Ruggeri, B. A. et al, Curr. Med. Chem. 1999, 6:845-857; Weeraratna, A. T. et al., The Prostate 2000, 45:140-148). Inhibition of the NGF-TrkA signaling pathway by small molecule TrkA inhibitors (Miknyoczki, S. J. et al., Clin. Cancer Res. 1999, 5: 2205-2212; George, D. J. et al., Cancer Res. 1999, 59: 2395-2401; Weeraratna, A. T. et al, Clin. Cancer Res. 2001, 7: 2237-2245) and anti-NGF antibodies (Miknyoczki, S. J. et al., Clin. Cancer Res. 2002, 8:1924-1931) has been postulated to inhibit not only growth, but also metastasis of neuroendocrine tumors in xenograft models. In addition, NGF has been shown to induce proliferation of endothelial cells (Cantarella, G. et al., FASEB J. 2002, 16: 1307). These cells, which form new vascular networks to feed the growing tumor, also express VEGFR2 tyrosine kinase receptors. Activation of these receptors by their ligands leads to endothelial cell proliferation, migration, and vessel formation and stabilization (Albo, D. et al., Curr. Pharm. Des. 2004, 10:27-37; Thurston, G., Cell Tissue Res. 2003, 31:61-68).
Certain diarylureas have been described as having activity as serine-threonine kinase and/or as tyrosine kinase inhibitors. The utility of these diarylureas as an active ingredient in pharmaceutical compositions for the treatment of cancer, angiogenesis disorders, and inflammatory disorders has been demonstrated. See Redman et al., Bioorg. Med. Chem. Lett. 2001, 11, 9-12; Smith et al., Bioorg. Med. Chem. Lett. 2001, 11, 2775-2778; Dumas et al., Bioorg. Med. Chem. Lett. 2000, 10, 2047-2050; Dumas et al., Bioorg. Med. Chem. Lett. 2000, 10, 2051-2054; Ranges et al., Book of Abstracts, 220th ACS National Meeting, Washington, D.C., USA, MEDI 149; Dumas et al., Bioorg. Med. Chem. Lett. 2002, 12, 1559-1562; Lowinger et al., Clin. Cancer Res. 2000, 6(suppl.), 335; Lyons et al., Endocr.-Relat. Cancer 2001, 8, 219-225; Riedl et al., Book of Abstracts, 92nd AACR Meeting, New Orleans, La., USA, abstract 4956; Khire et al., Book of Abstracts, 93rd AACR Meeting, San Francisco, Calif., USA, abstract 4211; Lowinger et al., Curr. Pharm. Design 2002, 8, 99-110; Regan et al., J. Med. Chem. 2002, 45, 2994-3008; Pargellis et al., Nature Struct. Biol. 2002, 9(4), 268-272; Carter et al., Book of Abstracts, 92nd AACR Meeting, New Orleans, La., USA, abstract 4954; Vincent et al., Book of Abstracts, 38th ASCO Meeting, Orlando, Fla., USA, abstract 1900; Hilger et al., Book of Abstracts, 38th ASCO Meeting, Orlando, Fla., USA, abstract 1916; Moore et al., Book of Abstracts, 38th ASCO Meeting, Orlando, Fla., USA, abstract 1816; Strumberg et al., Book of Abstracts, 38th ASCO Meeting, Orlando, Fla., USA, abstract 121; Madwed J B: Book of Abstracts, Protein Kinases: Novel Target Identification and Validation for Therapeutic Development, San Diego, Calif., USA, March 2002; Roberts et al., Book of Abstracts, 38th ASCO Meeting, Orlando, Fla., USA, abstract 473; Tolcher et al., Book of Abstracts, 38th ASCO Meeting, Orlando, Fla., USA, abstract 334; and Karp et al., Book of Abstracts, 38th AACR Meeting, San Francisco, Calif., USA, abstract 2753.
Despite the advancements in the art, there remains a need for cancer treatments and anti-cancer compounds.